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TOPIC: Powered Aluminum Dragon

Powered Aluminum Dragon 30 Oct 2016 00:54 #1005

Vertical Stabilizer work:

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Powered Aluminum Dragon 04 Nov 2016 00:08 #1007

For the most part done with the vertical tail. Needs fabric, holes drilled for mount fittings and for cables. The original wood/carbon reinforced is published at 5 lb in the builder's manual. This came in at 5.4 lb.



I now have to finish the design for the mounting fittings, and mount them and the assembly to a 4x4 post for the limit load test. Limit load for this assembly is approximately 200 lb. (12 lb/sq ft) This will be a much more severe test than the horizontal tail as the load is all cantilevered.
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Last edit: by Don B.

Powered Aluminum Dragon 24 Nov 2016 01:18 #1010

The Load test failed....I really screwed up in the design and stress analysis. I am not sure how much of the vertical tail I will be able to salvage, worst case the fittings only, but I think after I get back to it I may be able to use lots more. There were many good learning experiences with the this test. It will be a while before I will post again....sorry.

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Powered Aluminum Dragon 02 Jan 2017 21:39 #1011

I have been working to re-build the vertical stabilizer. I have hopefully found what I did wrong and fixed it. This spar is 8 times stronger than the last one, and I have gained 1 1/2 #or or so a little more weight. Shown is the mounting for the load test, the failure, and damage and some of the repair along with the new stabilizer spar going forward with the build.

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Last edit: by Don B.

Powered Aluminum Dragon 03 Jan 2017 01:28 #1012

interesting way to line up the center of the LE, it is difficult to determine the exact center after bending as the skin could have shifted in the vacuum bag and any slight twist or offset will throw off the center location of the LE. Pictures: Vacuum bag, LE hanging from pipe, Plumb bobs around pipe to center up skin, measure in from each side, assembly going forward.
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Powered Aluminum Dragon 03 Jan 2017 11:33 #1013

Ouch!

If it's any consolation, I know the feeling. My first carbon leading edge skin for one wing came out of the mold and looked perfect... except along the apex of the leading edge itself where there was significant bridging... resulting in it ending up in the bin. One of the layers in my infusion stack (possibly the peelply or the vacuum bag itself) was constained in some way and prevented the vac-bag from pressing into the apex of the curve. The same thing happened on my first attempt to infuse the tail fin leading edge, despite my earlier experience and best efforts. Expensive!!

Following those two screw-ups I modified the way I assembled the infusion stack and achieved perfection :-)

A material's maximum compressive strength can only be achieved if it can be prevented from buckling. Maintaining stiffness is the other side of the equasion. I was amazed at the difference in stiffness between the various grades of carbon cloth when I was making test samples for my leading edges and spars. Two different types of carbon cloth performed totally differently to each other. One was a 200gsm, non-woven, bi-axial cloth with a low modulous and the other was a 195gsm twill weave with a medium to high modulous. The bi-axial (which I expected to perform better) was very bendy and totally unsuitable, while the medium-high modulous twill cloth was at least 5-10 times stiffer (my subjective measure.) While the bi-axial may have been fine for use in my spars, it would have been useless in the leading edges. For simplicity I used the twill cloth throughout my build.

I see the spar cap under compression buckled and failed between two ribs, as might be expected. How did you stiffen your spar (caps/web) when you repaired the damage?

Stiffness can be dramatically improved by adding 'thickness' to a part without adding significant weight. In my case, all my spars are fabricated using just two layers of 195gsm twill cloth (cut at +/-45deg) and are very light and bendy. They are stiffened by the fore and aft ribs bonded to the shear web and between each pair of ribs by a strip of light weight foam board (25mm wide x 5mm thick) are laminated between the two layers of cloth. This significantly stiffens the shear web without adding much weight. The spar caps are stiffened both by the carbon rods that are encapsulated between the two layers of cloth and further by the leading edge, where it is bonded to the spar caps, lending horizontal and torsional stiffness.

Thanks for sharing your results - failures are every bit as important as successes, 'cos that's where we learn!

Keep going - you'll get there!

Phil.

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Last edit: by Phil Lardner.